1. Field of the Invention
The present invention relates to improved composite fibers and fabrics and methods for producing them. More particularly, the present invention relates to an improved composite textile of fiberglass and polytetrafluoroethylene (PTFE).
2. Description of Related Art
Fiberglass textiles are widely employed today in numerous applications. This is due to the many favorable properties of fiberglass, including relatively low cost, excellent mechanical strength, dimensional stability, good insulative properties, and excellent resistance to temperature and humidity. Among the popular present uses of fiberglass are as an architectural fabric, in the electronics industry (e.g. as a printed circuit board), as a filtration media, and as a structural composite.
Due mostly to its relatively low cost, fiberglass presently dominates the high temperature filtration market (typically defined as those filters operating within 300.degree. to 500.degree. F). In this regard, fiberglass often costs 33 to 95% less than some competitive synthetic textile fibers (e.g. polytetraethylene, aramids, polyphenylene sulfide, polyimides and copolyimides).
Although fiberglass performs adequately in these applications, it suffers from numerous deficiencies. Perhaps the greatest problem with fiberglass is that it is quite fragile--being easily damaged when flexed or abraded. As a result, fiberglass fabric is incapable of performing in many applications. For instance, where a filter must be vigorously flexed to free filtrate and clean the filter media (e.g. in a "shaker"-type bag house filter or a pulse-jet bag house filter), a fiberglass fabric will quickly fail. Even under less demanding regenerative procedures (e.g. reverse air cleaned bags), where far less bag flex is encountered, fiberglass has relatively limited operational life.
Another deficiency of fiberglass is that it is subject to certain chemical attack. Chemicals attack the glass filaments in the textile primarily when the process gas phase goes through a dewpoint excursion. Chemical attack can also occur in the gaseous phase or when solid particulate contacts the fiberglass.
In an effort to address some of the problems of chemical attack, a number of finishes and protective coatings have been developed. Examples of such treatments include constituents of silicone oils, graphite and PTFE dispersion coatings. Although such treatments have proven relatively effective at protecting fiberglass from chemical attack, they do not improve the problem of flex failure.
Another common problem with fiberglass is that it is difficult to handle and work. By way of example, if the fiberglass is not carefully handled during a weaving process, the low abrasion resistance of the fiberglass often leads to friction damage to the glass fibrils. Likewise, abrasion caused by weaving equipment can result in surface imperfections (e.g. glass pills) which can cause problems in later processing. Further, even a single fold in the glass material during processing can lead to fatigue and later failure.
In light of these many problems, synthetic fibers are the fibers of choice where long filter life is needed and/or extreme operative conditions are expected. Unfortunately, the costs of synthetic fibers restrict their accepted uses. Additionally, certain synthetic fibers, while having many exceptional characteristics, are also limited in certain respects. For example, PTFE tends to have stability (creep) problems in reverse air bag houses, with tension on the bag elongating it to a point at which proper cleaning and flexure does not occur. Copolyimides and aramids hydrolyze in the presence of moisture and high temperatures. Polyphenylene sulfide oxidizes and embrittles when exposed to oxygen and high temperature.
Accordingly, it is a primary purpose of the present invention to provide an improved fiber composite which retains many of the desirable properties of fiberglass, but which is far more resilient to flex, abrasion, and chemical attack.
It is a further purpose of the present invention to provide a fiberglass composite material which can be thoroughly handled and worked without fear of compromising its structural integrity.
It is another purpose of the present invention to provide a relatively low-cost composite material which has many of the desired properties of existing synthetic materials, such as long product life and resistance to chemical attack.
These and other purposes of the present invention will become evident from review of the following specification.